Disk packs, each consisting of a stack of spaced-apart rigid magnetic recording disks, have long been in widespread use as memories for electronic computers. Users have become accustomed to cleaning the recording surfaces of the disks periodically with a cloth containing isopropyl alcohol. About five years ago, a new style of disk pack began to be marketed which is called a data module. In contrast to the earlier packs wherein the heads are normally out of contact with the disks, the heads of the data module are in contact with the disks until the disks approach operating speed. This contact requires that the disks be lubricated. It is believed that the most widely used lubricants for the disks are members of a class of highly fluorinated polyethers having the repeating unit EQU --CF.sub.2 --O--
or EQU --CF.sub.2 --CF.sub.2 --O--
or ##STR1## for example, polyethers such as ##STR2## where n is an integer providing a Ferranti-Shirley viscosity (hereinafter measured at 1640 sec.sup.-1) of about 75-1350 centipoises. Compare U.S. Pat. Nos. 3,778,308 (Roller) and 3,919,719 (Wright). Such polymers are available commercially from E. I. duPont de Nemours & Co. as "Krytox" 143 fluorinated oils. A preferred member of this class has been "Krytox" 143 AD which has a Ferranti-Shirley viscosity of 1322 centipoises and reportedly has a viscosity index (ASTM D2270) of 145 and an average molecular weight of about 7000. When these fluorinated polymers are used to lubricate rigid disks they tend to be removed if the disks are cleaned with isopropyl alcohol.
Some manufacturers of data modules buy prelubricated disks which may become contaminated during shipment and handling and hence need to be cleaned. If such cleaning were to remove the lubricant, the data modules would soon fall. The recording layers of the disks, which typically are thin coatings of fine magnetizable particles in a thermoset epoxy resin matrix, would prematurely wear away where contacted by the heads, and the matrix resin would gradually transfer to the heads to interfere with their flying capability.
The next generation of rigid disk equipment may employ heads which permanently remain in contact with the recording surface, in which case premature removal of the lubricant would be even more troublesome.